The application of security on documents has always been a delicate balancing act between ease-of-use and adequate protection for the document's contents. When the documents contain commercial content, insufficient security can mean lost income, when the protected content is sensitive confidential information, the consequences can be far more dire. On the other hand, if product documentation were to be password-protected, users may not be able to access it.
As an example, by way of a security policy associated with a document, it's possible to limit printing, the selection (and hence, copying) of text and image, prohibit changing the document or merging with other documents, and to prevent users from filling form fields or digitally signing a document. It is also possible to separately encrypt a document and its attachments. There are additional security measures available: depending on the needs of the document distributor, it's also possible to digitally sign a document to indicate approval and prevent changes from being made to the document, incorporate real-time authentication of a document each time someone attempts to open it and to limit the number of times a document can be opened.
A policy server, for example the Adobe® LiveCycle™ Policy Server (ALPS) available from Adobe Systems Incorporated of San Jose, Calif., allows for the creation, administration, application and authentication of security policies. A security policy is a configurable, re-usable profile that defines security settings that can be applied to a document. Security policies define the usage rights of a document. For example, security policies define who can open, print, edit or fill-out the file. Once a security policy is applied to a document, it becomes a part of the document, meaning that the document will retain its security no matter how many times it is passed on or distributed.
A policy server can be used to create new security policies or apply existing policies, and further can act as a web-based authentication engine. Documents configured to communicate with the Policy Server-enabled server in this way can have their permissions managed dynamically by the document provider.
Before a recipient can access the document, the policy server first authenticates the recipient's identity against credentials stored in the organization's directory. Then, using the appropriate software (e.g. Acrobat® or the Adobe® Reader® software), the user may use the document according to the controls established in the policy. This also means that permission for a given document can be revoked simply by updating the policy on the server. This solves the problem of revoking the security access of ex-employees or those that change their role within an organization. For offline access, it's also possible to set document expiration dates, where users are allowed time-limited or subscription-based access to a given document or set or documents. This forces recipients who desire continued use of protected content to request additional offline access from the document provider once their expiration dates have been reached. This time-limiting feature can also be very useful when it's crucial to have current information, as documents can be set to expire once their content becomes obsolete.
Keeping track of documents is also important, and ALPS also supports an automated document auditing feature. This can be used to track the recipient's use of a protected document, and monitors what happened to the document and when.
Documents can include a code such as a barcode which is a machine-readable representation of information in a visual format on the document. Originally barcodes stored data in the widths and spacings of printed parallel lines, but today they also come in patterns of dots, concentric circles, and hidden in images. Barcodes can be read by optical scanners called barcode readers or scanned from an image by special software. Barcodes are widely used to implement Auto ID Data Capture (AIDC) systems that improve the speed and accuracy of computer data entry.
While traditionally, barcodes encoding schemes represented just numbers, newer symbologies add new characters such as from the upper case alphabet to the complete ASCII character set and beyond. The drive to encode ever more information in combination with the space requirements of simple barcodes led to the development of matrix codes (a type of 2D barcode), which do not consist of bars but rather a grid of square cells. Stacked barcodes are a compromise between true 2D barcodes and linear codes, and are formed by taking a traditional linear symbology and placing it in an envelope that allows multiple rows.
A QR Code is a matrix code (or two-dimensional bar code). Although initially used for tracking parts in vehicle manufacturing, QR Codes are now used for inventory management in a wide variety of industries. More recently, the inclusion of QR Code reading software on camera phones has led to a wide variety of new, consumer-oriented applications, aimed at relieving the user of the tedious task of entering data into their mobile phone. QR Codes storing addresses and URLs are becoming increasingly common in magazines and advertisements. The addition of QR Codes on business cards is also becoming common, greatly simplifying the task of entering the personal details of a new acquaintance into the address book of one's mobile phone.
Another type of code is known as a glyph. A glyph is a particular graphical representation of a grapheme, or sometimes several graphemes in combination, or only a part of a grapheme. A grapheme designates the atomic unit in written language. Graphemes include letters, Chinese ideograms, numerals, punctuation marks, and other symbols. In a phonological orthography a grapheme corresponds to one phoneme. In spelling systems that are non-phonemic—such as the spellings used most widely for written English—multiple graphemes may represent a single phoneme. In computing as well as typography, the term character refers to a grapheme or grapheme-like unit of text, as found in natural language writing systems (scripts). A character or grapheme is a unit of text, whereas a glyph is a graphical unit.
TeX is a typesetting system designed to allow anybody to write high-quality books using a reasonable amount of effort, and to provide a system that would give the exact same results on all computers. TeX is popular in academia, especially in the mathematics, physics and computer science communities. For example, the sequence ffi contains three characters, but will be represented by one glyph in TeX, since the three characters will be combined into a single ligature. Conversely, some typewriters require the use of multiple glyphs to depict a single character (for example, two hyphens in place of a dash, or an overstruck apostrophe and period in place of an exclamation mark).
Most glyphs in typography originate from the carved and cast characters of a typeface, also called a font. In computing, font refers to a typeface manifesting as an indexed collection of glyphs or glyph-rendering instructions, and associated information that facilitates rendering mapping characters to glyphs and for rendering glyphs in different sizes. For a given typeface or font, each character typically corresponds to a single glyph. However, this is not always the case, especially in a font used for a language with a large alphabet or complex writing system, where one character may correspond to several glyphs, or several characters to one glyph.
Watermarking is a technique which allows an individual to add hidden copyright notices or other verification messages to digital audio, video, or image signals and documents. The hidden message is typically a group of bits describing information pertaining to the signal or to the author of the signal (name, place, etc.). The technique takes its name from watermarking of paper or money as a security measure. Digital watermarking is not a form of steganography, in which data is hidden in the message without the end user's knowledge, although some watermarking techniques have the steganographic feature of not being perceivable by the human eye.